After i finished the round of wiring work detailed in the previous post, I obtained the AWG #8 wire for the three phase leads, a neutral, and a ground, and ran them all out from the main panel, connecting to a 40 amp breaker. I had the electrician come by to take a look to see if i had gone wrong anywhere. We threw the safety switch on and the transformer roared to life. Well, it 'roared' like a mouse might roar - a very quiet hum was about all that came out of it. I was apprehensive it might be noticeably noisy, but such is not the case. That's good!
The electrician checked the output at the receptacles and I had 462v at each location. So, all good right? The electrician seemed satisfied and said I'd done a good job. Time to bask in the warm glow of success perhaps?
That evening I returned home to find an email from an avid reader of this blog who also happens to be an electrician. Having read my previous post he mentioned that there were a few things which were not done properly and filled in the details for me, quoting relevant sections from the code book.
So, on the one hand I have one electrician saying everything is fine, and another saying everything is not fine. What to do? Well, just like with medical advice, it made sense to get a third opinion. I called up a friend of mine in California who is a professional electrician with his own company. He concurred with the electrician who had written the email to me.
In a situation like this, the prudent thing to do seemed to be to err on the side of caution, and that is what I did. As it turns out, the National Electrical Code treats a transformer as if it is an entirely separate source of power apart from the main load centers, and thus it is wired up as if it were the service entry into the building. Even though I had run a ground wire over from the main panel to the transformer, the transformer was required to be grounded just like the main panel, which involved running a grounding conductor over to the building's main water supply piping, where it ties directly to the copper pipe. The building's main power connection is 120' away from where the ground connection is located, and thus a #4-0 aluminum grounding conductor is run all the way along to that point. I was surprised to find this incredibly long grounding conductor, but they had to do what they had to do. Normally it is better I'm sure to have a shorter run from the main panel to a suitable grounding point.
Anyway, I could run #6 copper as it does not require a conduit casing in that size. Here you can see the green ground wire run along the LiquidTuff flexible conduit on the start of its journey:
The wire runs up to the ceiling and travels a further 87' until it terminates at the water pipe. How do I know it is 87'? Well, I guessed that 90' was about right and came out with just 3' feet to spare, which was a fortunate outcome.
Here's the wall with the revised electrical component configuration:
Whereas before the output from the transformer went to a pair of receptacles, now there are individual fused safety switches in place, one for each receptacle/machine. I picked up the Square D safety switches and their fuses on Ebay for cheap. I also removed the neutral conductor from all of the equipment, and bonded the neutral terminal in the transformer to the transformer casing and attached the new green ground wire to the transformer's neutral terminal. This might seem odd to some out there to connect the neutral directly to the ground, however this in fact is exactly what happens at the main panel anyhow. The neutral and ground are kept separate in the system otherwise.
Now, I didn't take the electrician's recommendations strictly at face value, I did some research online, which is of course convenient but not always the best way to get to the truth of a thing. The electrician friend also sent me some links for further reading. There are no shortage of articles out there explaining the finer points of the NEC book it would appear. While the writing might be in English, and i know the meaning of individual words well enough, one does find the reading heavy-going at times, such as in this example taken from an article entitled "The Basics of Bonding and Grounding Transformers":
This path allows unintentional ground-fault current to flow from the point of a ground fault on the derived ungrounded circuit conductors, to the derived source, then back to the origin of the ground fault. This unintentional ground-fault current flow elevates the current in the transformer primary winding for ground faults between the derived source of the transformer and the first overcurrent protection device — or facilitates the operation of the transformer secondary overcurrent protection devices if the ground fault is on the load side of these devices.
Are you feeling woozy, or finding an urge to stare blankly? Well, that's how I found a lot of the reading on various electrical topics. Anyway, made it through to the other side and feel like I have a safe and perfectly operating - and quiet - transformer now installed.
Sharp-eyed readers may have also spotted some new dust collection piping also visible in the above photo. Putting that in soaked up another day or two, and involved a long trip down to New Haven CT to pick up the parts. The collector pipes are 10' long and cannot ship economically, so I made the trip.
Today was another adventure.
The Wadkin dimension saw had cleared customs in Boston late last week and was ready for pickup. They give you 5 days free storage of the item, and then start charging, and I believe the rate is $60/day. I arranged for a trucking company to go and get the item and deliver it to a tow truck company close to where my shop is located, but this proved to be too difficult a task for the trucking company. I always have some kind of dumb hassle when it comes to freight transactions. I'm not going to get into the rest of the rigamarole, but with one free day left, I had to take matters into my own hands. I rented a Penske moving van and drove to deep Boston today, right to the docks, and picked the machine up.
I got back to the shop in mid afternoon and a few hours later had the crate in my shop, roughly in position, and had started to unwrap the present:
I'll have more to say about the machine in a subsequent post as I get it up and running.
Thanks for dropping by the Carpentry Way! Comments always welcome.